The formation and role of vortices in protoplanetary disks.

We carry out a two-dimensional, compressible simulation of a disk, including dust particles, to study
the formation and potential role of vortices in protoplanetary disks. We found that anticyclonic vortices
can form out of an initial random perturbation of the vorticity held. Vortices have a typical decay time
of the order of 50 orbital periods (for a viscosity parameter a\10~4 and a disk aspect ratio of
H/r\0.15). If vorticity is continuously generated at a constant rate in the Now (e.g., by convection), then
a large vortex can form and be sustained (because of the merger of vortices). We found that dust concentrates
in the cores of vortices within a few orbital periods, when the drag parameter is of the order of the
orbital frequency. Also, the radial drift of the dust induces a significant increase in the surface density of
dust particles in the inner region of the disk. Thus, vortices may represent the preferred location for
planetesimal formation in protoplanetary disks. The relative difficulty in forming such vortices, however,
suggests that a further examination of this phenomenon is required in order to determine the viability of
vortices as planet formation sites. We show that it is very difficult for vortex mergers to sustain a relatively
coherent outward Nux of angular momentum.